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UNITED STATES E
NUCLEAR REGULATORY COMMISSION
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WASHINGTON. D.C. 20666 January 22, 1993 1
MEMORANDUM FOR:
Herbert Berkow, Director Project Directorate 11-2 Division of Reactor Projects 1/II FROM:
Robert Jones, Chief Reactor Systems Branch Division of Systems Safety and Analysis i
Christooher Grimes, Chief Technical Specifications Branch Division of Operating Reactor Support g
SUBJECT:
TECHNICAL ASSISTANCE REQUEST, CONTINUOUS CORE REACTIVITY MONITORING FOR COMBUSTION ENGINEERING REACTORS (TIA 92-022)
(TAC NOS. M84757/84758) 1 By letter dated October 22, 1992, from Ellis Merschoff (Reg. II) to Gus Lainas (DRP I/11), assistance was requested in resolving the need for and means of continuous core reactivity monitoring for St. Lucie 2 and for Combustion i
Engineering (CE) reactors in general. Specifically, the question of whether a l
technical specification (TS) change is needed to assure proper reactivity monitoring and control was raised, and if so, to initiate that change.
levels from 10', reactors contain excore monitors which sense leakage neutron In general, CE 4
% to 200% power. The system is divided into startup, control, and safety channels. The startup, or source ran or (SRM) channel covers shutdown and subpower neutron levels (10'ge moni}%).
to 10' The safety channels, or wide-range monitors, are divided into logarithmic and linear power channels and cover the subpower levels as well as the entire power range from 2x10 a to 200%.
The control channel yields information on core neutron level when the reactor is critical and supplying heat to the reactor coolant system and covers the range from I to 125%. The startup and safety channels overlap by at least one decade to prevent loss of indication when one range is operating at the high end of its scale and the next range is operating at the low end of its scale.
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i The St. Lucie TS as well as the current and improved CE Standard Technical Specifications (STS) require redundant source range monitoring capability to 4
detect changes in the reactivity condition of the core during refueling (Mode 6). Redundant neutron monitoring is required by the Wide Range Logrithmic Neutron Flux Monitor for Modes 1 through 5, as part of the reactor protection system (RPS) instrumentation LCO. These monitors provide continuous indication in the control room and are relied on for the mitigation by the operator of events such as an inadvertent boron dilution from shutdown conditions.
It is the Wide Range Logrithmic Power Level-High trip that protects the integrity of the fuel cladding and the reactor coolant pressure boundary in the event of an unplanned criticality from shutdown.
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j January 22, 1993 The issue of continuous core reactivity monitoring is of sufficient safety significance such that neutron flux monitoring requirements for all Modes are 1
discussed in the Bases of the CE Improved STS (ISTS).
ISTS 3.3.1, " Reactor Protection System (RPS) Instrumentation", addresses flux / power monitoring for j
Modes 1 and 2 as part of the RPS.
"[ Logarithmic] Power Monitoring Channels", addresses Modes 3, 4, and 5.
The requirements for source range neutron flux monitoring during refueling (Mode 6) are addressed in ISTS 3.9.2, " Nuclear Instrumentation".
No action is required to change either the current or improved STS.
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Robert ones, Chief Reactor Systems Branch I
i i Division of Systems Safety and Analysis, NRR 1i 1
Christopher Grimes, Chi f 3
Technical Specifications Branch j,
Division of Operating Reactor Support, NRR
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.. January 22, 1993 Pa issue of continuous core reactivity monitoring is of sufficient safety.
significance such that neutron flux monitoring requirements for all Modes are discussed in the Bases of the CE Improved STS (ISTS).
ISTS 3.3.1, " Reactor Protection System (RPS) Instrumentation", addresses flux / power monitoring for Modes I and 2 as part of the RPS.
ISTS 3.3.13, "[ Logarithmic] Power i
Monitoring Channels", addresses Modes 3, 4, and 5.
The requirements for source range neutron flux monitoring during refueling (Mode 6) are addressed in ISTS 3.9.2, " Nuclear Instrumentation".
No action is required to change either the current or improved STS.
1 Original syned By i
j Robert C. Jones, Chief Reactor Systems Branch Division of Systems Safety and Analysis, NRR i
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Division of Operating Reactor Support, NRR ii DISTRIBUTION:
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